>I am amazed at the lack of thought (I mean science) behind
>statements which frequently are repeated here. In the past years,
>this has been discussed and validated on this forum, and in
>professional RF power practice its not even a question to
>regurgitate, and yet, here it is again.
>As a professional involved in RF amplifier designs, I completely
>support and agree with Ian White's reply and references listed at the
>bottom of this note, and have also presented physical evidence in the
>way of photographs of the insides of tubes which have arced (2 weeks
// Your photographs of what occasionally takes place at c. 30kV are
impressive, John. In Sept.-Oct, 1990, *QST*, and on my Web site, I
presented physical evidence of what occasionally takes place at 2.5 - 4
kV. Not all of the tubes shown were damaged by an oscillation condition.
>They were not due to parasitics. Energy is energy. Whether
>we have 3kV with 80 uF or 30 kV with 80 uF of capacitance.
// I own a 0-30kV DC power supply. At full-throttle, conductors glow
blue in the dark. Ozone permeates the air. If a tube under test
conducts current at 30kV, X-radiation occurs. 30kV is a whole nuther
> I pointed out that in the latter case, one MUST use an active shunt crowbar
>device in addition to series resistance. In ham sized tubes, series
>resistance alone may work. But the cause of an unexplained discharge
>within the envelope of a vacuum tube is NOT always because of an
// True, John. The issue at hand is bent/broken thoriated-tungsten
filaments and gold evaporation from grids. In my opinion, tungsten is
not easily bent and gold is not easy to boil,
>Gas pressures inside a tube may change from
>effects from high voltage conditioning, changing RF level, DC
>current, load VSWR. We should ask other EE's and RF practicioners who
>design amplifiers to speak here; unfortunately, most will shun the
>unprofessional approach of the 'scientific' method as practiced on
>many internet discussions and won't bother.
// During the Grate Parasitics Debate, Buzz Miklos, the R&D Engineering
Manager at Eimac's Salt Lake City plant was scheduled to appear on the
debate to scientifically expose the numerous technical errors in my QST
articles. However, I thought that something smelled a tad fishy, so I
telephoned the personnel department at the plant and discovered that the
"Manager" was never higher up than the bottom rung of the engineering
ladder. After word of this leaked out, the "Manager" proved to be a no
show. Subsequently, I found out that this person is an amateur radio
operator, and that he handed out business cards at hamventions
identifying himself as said R&D Engineering Manager. (transcripts of
this rather jolly debate are available from Yours Truly)
>I have attempted to give my own experiences to this forum. I
>certainly haven't built as many amateur amplifiers as many here. Or
>troubleshooted them. It is extremely frustrating to read people
>preaching stuff which they believe in like religious zealots. We have
>enough of them in the news in the USA right now.
>On 8/30, Richard Measures <2> responded this way:
>JL first stated:
>"I recommend that hams consider other methodologies which can cause
>arcs besides an 'all inclusive' parasitic theory....
> <2> replied to this:
>"// The all inclusive parasitic theory originated with ....."
// Mr. "...." stated that nickle-chromium alloys have more RF-resistance
as frequency decreases, that AC circuit-analysis does not work for L-R
VHF suppressors, that gas can disappear in cold tubes, and that he's one
of our recognized amplifier experts (p.72, 9-94 QST).
- John: Who redacted the name of Mr, "....." ? Do you know why?
>"in industry we don't subscribe to that theory."
>"//nor do I"
>OK, we finally hear that there are other possibilities in mind?
>To which <2> wrote yesterday:
>>// The purpose of the glitch-R is to protect the electron tube from
>>failure during an intermittent oscillation condition.
>> A suitable glitch resistor in series with the positive HV bus will happily
>>do this job - but only for those who have more brains than money.
>Ian White wrote:
>> >>Make that "...from failure due to a current surge occurring for *any*
><2> (Richard Measures) wrote:
>> >// Please name and explain some other causes of potentially fatal
>>>current surges, Mr. White.
>Ian White replied:
>>You appear to have forgotten that this very subject was discussed at
>>some length back in January/February.
>>Here are a few quotes from the literature.
>>"Although a very high degree of insulation between two electrodes can be
>>obtained... by modern high-vacuum technique, it is nevertheless possible
>>for this insulation to break down spontaneously and completely. This
>>phenomenon is known by various names, such as... the "Rocky Point
>>effect", after the American wireless station, which is one of several at
>>which it has been observed. ... Time lags [after application of
>>voltage] can vary between a few seconds or minutes to tens, hundreds or
>>even thousands of hours."
>>Gossling (British GEC), 'The Flash-Arc in High Power Valves', 1932.
>>"Most power tubes are subject at some time to a phenomenon known as the
>>Rock Point effect, which derives its name from experiences with power
>>tubes in communications transmitters at Rocky Point, Long Island.
>>This phenomenon manifests itself as an internal flash-arc developing
>>with little warning on power tubes which apparently are of good design
>>and operated in a conservative manner... The cause of this phenomenon is
>>not thoroughly understood..."
>>Parker and Hoover (RCA), 'Gas Tubes Protect High-Power Transmitters',
>>"An arc is a self-sustaining discharge of electricity between electrodes
>>in a vacuum environment... Since any high voltage vacuum device may arc
>>at one time or another..."
>>Eimac, 'Fault Protection', Application Bulletin #17, 1987.
>FAQ on WWW: http://www.contesting.com/FAQ/amps
>Administrative requests: amps-REQUEST@contesting.com
- R. L. Measures, 805.386.3734, AG6K, www.vcnet.com/measures.
FAQ on WWW: http://www.contesting.com/FAQ/amps
Administrative requests: amps-REQUEST@contesting.com